Micro viscometer

ABSTRACT

Disclosed is a micro viscometer comprising a body including an inlet where a fluid flows in, an outlet where the fluid flows out, a first chamber and a second chamber that is connected to the inlet and the outlet, respectively, a substrate and a cover that partition multiple micro channels that connect the first chamber and the second chamber; a first thin film that vibrates with the fluid within the first chamber and locates on the side of the first chamber; a second thin film that vibrates with the fluid within the second chamber and locates on the side of the second chamber; an actuating part that applies vibration onto the fluid within the first chamber by conducting vibration through the first thin film; a sensing part that senses vibration or pressure onto the fluid that transfers through the micro channels to the second thin film through vibration of the first thin film.

TECHNICAL FIELD

This present application relates generally to a Micro Viscometer, adevice for measuring the viscosity of fluids.

BACKGROUND ART

Generally, viscosity is a coefficient that expresses the physicalproperty of the fluid viscosity volume, and various types of viscometersare developed and used to measure this type of viscosity.

A viscometer called the Greenspan viscometer (Refer to M. Greenspan andF. N. Wimenitz, “An Acoustic Viscometer for Gases-I,” NBS Report 2658(1953)), which was invented in 1953 by Greenspan and Wimenitz to measurethe viscosity of gas with a design that comprises of two HelmholtzResonators that are attached and face each other, exists, however, thisviscometer relatively takes up much space and the performance shows a38% error margin that was considered not to be suitable structure.

In 1996, K. A. Gillis came up with a more precise viscometer, comparedto the Greenspan viscometer, by going through an experimental error andcorrection process to reduce the errors within the range of ±0.5% andderive more accurate gas viscosity measurements. (Refer to R. A. Aziz,A. R. Janzen, and M. R. Moldover, Phys. Rev. Lett. 74, 1586 (1995))

However, issues for this method existed, where the valid frequencysection for this method was limited only to the low frequency domain.For example, the viscometer designed by K. A. Gillis could only beapplied to low frequency under 200 Hz. The reason for this phenomenonwas because the Helmholtz Resonator was applied assuming that theproduct of the wave number of the sound wave and the characteristiclength was greatly smaller than 1. Furthermore, due to the fact that nomeasurements were made for liquids, the measurements were restricted togas and the size was large that required a mass amount of fluid.

Also, U.S. Pat. No. 6,141,625 discloses a viscosity module with acrystal resonant sensor, where this module relates to a mobileviscometer that can measure the viscosity of the fluid even with a smallquantity of reagent. This viscometer utilizes a disk type thin crystalfilm for the viscosity sensor.

To obtain this type of crystal resonant frequency, the sensor operatesin thickness shear mode by positioning electrodes on the top and bottomportion of the thin film and passing a signal. If a certain liquidexists on the top surface of the crystal, then power loss occurs thatcause damping in the crystal resonant frequency. Eventually, theviscosity of the liquid can be measured by checking the value ofdamping.

However, accurate measurements are only obtainable when a viscositymodule with a crystal resonant sensor is placed horizontally, liquid isequally distributed and a large amount of liquid. In other words, theviscosity module with a crystal resonant sensor needs several ml ofliquid with assuming that the volume of a single water drop is 0.04 mland an issue exists where it is impossible to take measurements with thevolume of a single water drop. Furthermore, this type of viscometer hasdemerits that it is impossible to make measurements of gas, since itutilizes the gravity applied on liquids.

On the other hand, many forms exist for viscometers that use thecapillary tube, however, most viscometers utilize the differential headcaused from gravity as it is disclosed in U.S. Pat. Nos. 6,322,624,6,402,703, 6,428,488, 6,571,608, 6,624,435, 6,732,573, and 5,257,529,etc. Due to the reason that the viscometer uses the differential head,measurements are limited to liquids, furthermore, issues in the amountof liquids needs exist even if capillary tubes, where the volume ofliquids necessary is more than a couple dozen to hundreds of ml that isregarded to be a large amount.

SUMMARY

A first embodiment of the present invention regarding a micro viscometercomprises a body including an inlet where a fluid flows in, an outletwhere the fluid flows out, a first chamber and a second chamber that isconnected to the inlet and the outlet, respectively, a substrate and acover that partition multiple micro channels that connect the firstchamber and the second chamber; a first thin film that vibrates with thefluid within the first chamber and locates on the side of the firstchamber; a second thin film that vibrates with the fluid within thesecond chamber and locates on the side of the second chamber; anactuating part that applies vibration onto the fluid within the firstchamber by conducting vibration through the first thin film; a sensingpart that senses vibration or pressure onto the fluid that transfersthrough the micro channels to the second thin film through vibration ofthe first thin film.

The resonant frequency of the first thin film may be identical to theresonant frequency of the second thin film.

At least one side within the inlet, the outlet, the first chamber, thesecond chamber and the micro channels may be coated with hydrophiliclayer.

Each of multiple micro channels that connect the first chamber and thesecond chamber has substantially the same length.

The actuating part may include a first piezoelectric layer and firstelectrodes disposed on each side of the first piezoelectric layer.

The sensing part may include a second piezoelectric layer and secondelectrodes disposed on each side of the second piezoelectric layer.

The substrate may include a silicon layer and a material of the covermay be a transparent material.

A second embodiment of the present invention regarding a microviscometer comprises a first chamber and a second chamber that arepositioned at intervals; multiple micro channels that connect the firstchamber and second chamber; a first thin film and a second thin filmthat are arranged on the first chamber and the second chamber,respectively, and that hold the same resonant frequency each other; anactuating part that applies pressure to the first thin film; and asensing part that detects the pressure applied to the second thin film.

A volume value of the first chamber may be substantially identical tothat of the second chamber.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in accordance with the first embodimentof the present invention illustrating a micro viscometer.

FIG. 2 is an end view of the first embodiment of the present inventionillustrating a micro viscometer.

FIG. 3 is a graph used to explain the method of measuring the viscosityusing resonant frequency from a micro viscometer, according to oneembodiment of the present invention.

FIG. 4 is a graph used to explain the method of measuring the viscosityof the fluid using resonant frequency from a micro viscometer, accordingto one embodiment of the present invention.

FIG. 5 is a graph comparing the difference of results between thecalculation method of the Helmholtz resonator when ka<<1 and thecalculation method according to one embodiment of the present inventiondisregarding the value of ka.

FIG. 6 is a cross-sectional view of the second embodiment of the presentinvention illustrating a micro viscometer.

FIG. 7 is a graph of the absolute difference of acoustic pressureaccording to the number of micro channels when the viscosity of thefluid changes, based on the first embodiment and second embodiment ofthe present invention.

FIG. 8 is a graph of the variation rate of acoustic pressure accordingto the number of micro channels in identical conditions with FIG. 7.

FIG. 9 is a diagrammatic view of the chamber structure of a microviscometer according to one embodiment of the present invention.

FIGS. 10 a-10 b are diagrammatic views of the first resonant frequencyand second resonant frequency that are transferred within the chamber ofa micro viscometer, respectively.

FIG. 11 is the electric circuit of a micro viscometer according to oneembodiment of the present invention.

FIG. 12 is the trench structure of a micro viscometer according to oneembodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view in accordance with the first embodimentof the present invention illustrating a micro viscometer and FIG. 2 isan end view of the first embodiment of the present inventionillustrating a micro viscometer.

As illustrated, a micro viscometer 100 positions 2 Helmholtz resonatorsin parallel so that viscosity can be measured even with a small amountof fluid. The micro viscometer comprises substrate a thin film 150, anactuating part 170 and a sensing part 180, a body 110 that includes asubstrate 113 and a cover 114.

The substrate 113 and the cover 114 are bonded onto the body 110 with aninterval to provide space for an inlet 111, an outlet 112, a firstchamber 120, a second chamber 130 and a micro channel 140.

The substrate 113 can be composed of a Silicon On Insulator (SOI) thatpossess a Silicon single crystal layer on top of the silicon wafer orinsulator, and space for the first chamber 120 and the second chamber130 prepared through the Deep Reactive Ion Etching (DRIE) process isprovided one side of the substrate 113.

Anodic bonding is operated on the cover 114 and the substrate 113 sothat decay space is given to the inlet 111, the first chamber 120, thesecond chamber 130, the outlet 112 and the micro channel 140. Also, amaterial of the cover 114 may be transparent material such as a glass tovisually confirm a fluid within the cover 114.

On one side of the inlet 111 and the outlet 112 of the body 110,open-close valves 191, 192 are provided so that fluids inputted withinthe body 110 does not flow outside. To open-close the fluid movement,open-close valves 191, 192 may be omitted according to a method ofmeasuring the viscosity of the fluid.

The first chamber 120 and the second chamber 130 of the body 110 arespacially connected to the inlet 111 and outlet 112, respectively. It isdesired for the first chamber 120 and the second chamber 130 to haveidentical volume and height. The design is to minimize an error that mayoccur from the vibration applied on the thin film 150, 160 whenmeasuring the viscosity of the fluid.

The micro channel 140 connects the first chamber 120 with the secondchamber 130 and provides space for viscosity loss of the fluid whenmeasuring the fluid viscosity within the body.

The thin film 150, 160 is positioned on the substrate 113 so that it caneach cover the first chamber 120 and second chamber 130. The thin film150, 160 separates the first chamber 120 and the second chamber 130 fromthe outside and at the same time vibrates with the filled fluids withinthe first chamber 120 and the second chamber 130. This type of thin film150, 160 is formed in a single film, as illustrated, however, it canhave additional two thin films for the first chamber 120 and the secondchamber 130, correspondingly.

Furthermore, the thin film 150, 160 is formed with Silicon Nitride (SiN)laminated onto the Silicon wafer, and comprises an insulator 153, 163attached to the top and bottom of the silicon wafer 151, 161 asillustrated.

It is suitable to use a Si type insulator such as Silica dioxide (SiO2)as the insulator 153, 163.

The actuating part 170 locates on the first thin film 150 thatcorresponds to the first chamber 120 and conducts vibration onto thefirst thin film 150 so that the vibration can transfer to the fluidwithin the first chamber 120.

The actuating part 170 comprises a first electrode 175, a piezoelectriclayer 171 arranged on the first electrode 175 and a second electrode 173that is positioned on the piezoelectric layer 171. One side of thesecond electrode 173 is separated with the first electrode 175 andconnected to the first thin film, while the other side of the secondelectrode 173 is located on the first piezoelectric layer 171.

The sensing part 180 comprises the second thin film 160 that correspondsto the second chamber 130 and senses the vibration or the pressure ofthe fluid within the second chamber 130 that is transferred to thesecond thin film 160.

This type of sensing part 180, similar to the actuating part 170,comprises a third electrode 185 disposed on the second thin film and asecond piezoelectric layer 181 arranged on top of the third electrode185 and a fourth electrode 183 positioned on the second piezoelectriclayer 181. Thus, one side of the fourth electrode 183 is separated fromthe third electrode 185 and connected to the second thin film, while theother side of the fourth electrode 183 is arranged on one side of thesecond piezoelectric layer 181.

Meanwhile, the actuating part 170 and the sensing part 180 for examplehave used the piezoelectric layer for piezoelectric effects, however, itis not limited to this example and polymer materials with piezoelectriccharacteristic can also be utilized.

During operation, fluid, such as air, within the body 110 outflowsthrough the outlet 112 to the outside, the inside pressure decreases andthe fluid inflows within the body 110 through the inlet 111

It is suitable to have Hydrophilic surface treatment such as hydrophiliclayer done on at least one side of the compositions within the body 110of a micro viscometer 100 where it has contact with the fluid such asthe inlet 111, outlet 112, first chamber 120, second chamber 130 andmicro channel 140. This helps the inflow of the fluid within the bodyand prevents air bubble formation within the body that may occur fromsurface tension of the fluid.

On the other hand, open-close valves 191, 192 are shut off when thefluid fills the body 110 so that it can prevent the fluid to flowoutside from the body 110 interior.

Next, by providing the voltage (V_(input)) as a Sine function similar toEquation 1 below in the frequency domain that includes resonantfrequency of the system of a pair of first electrode 175 and secondelectrode 173 of the actuating part 170, the first piezoelectric layer171 applies vibration to the first thin film.V _(input) =V ₀ sin_(ω) I  Equation 1

When the first thin film vibrates, a loss in sound wave occur due to theacoustic boundary layer inside the micro viscometer, or in other wordsthe inside the body 110. This type of loss can be categorized into two;one is the loss(α_(v)) of the viscosity boundary layer(δ_(v)) within themicro channel that has the fastest particle velocity and the other isthermal loss(α_(t)) that comes from the thermal boundary layer(δ₁) ofthe first chamber 120 and second chamber 130 that has large area tovolume ratio.

When the viscosity boundary layer or the thermal boundary layer isgreatly smaller than the radius or half the height, r_(c), of the microchannel 140 this loss of the boundary layer has the relationship withthe Q factor as shown in Equation 2.

$\begin{matrix}{\frac{1}{Q} = {{\frac{\alpha_{v}}{2\;\pi} + \frac{\alpha_{t}}{2\;\pi}} = {\frac{\delta_{v}}{r_{c}} + {\left( {\gamma - 1} \right)\frac{\delta_{t}S}{\pi\; V}}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

In this equation, the r is the ratio of specific heat of the fluid, s isthe area of the chamber, v is the volume of the chamber, δ_(v) is thethickness of viscosity boundary layer of the micro channel 140 interior,δ_(t) is the thickness of thermal boundary layer of the chamber 120,130.

The sound wave conveys to the second thin film possessing this loss andthe frequency response outputted from the second thin film from theeffects of the second piezoelectric layer 181 of the sensing part 180can be measured.

When measuring the Q factor for this type of frequency response Equation2 is used to measure the viscosity of fluid as shown in Equation 3.

$\begin{matrix}{v = {\frac{\mu}{p} = {\frac{\omega\; r_{c}^{2}}{2}\left\{ {\frac{1}{Q} + {\left( {1 - \gamma} \right)\frac{\delta_{t}S}{\pi\; V}}} \right\}^{2}}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

In this equation, v is the Kinematic Viscosity, μ is the DynamicViscosity and ρ is the density.

Alternatively, a different method can be introduced, as discussed below,using a micro viscometer 100 according to one embodiment of the presentinvention, which is the Single-Frequency Driving Method (SFDM) that usessingle frequency (or resonant frequency) to measure the viscosity.

For the method for measuring the viscosity from single frequency, amethod for measuring the change or the viscosity of the fluid utilizingthe frequency (or resonant frequency) instead of the Q factor is used toovercome onerous tasks of using sweeping on the frequency domain thatapplies the Q factor and finds the resonant frequency and directlyobtains the half power band width, and also accurately deriving the Qfactor due to the error of the resonant frequency or half powerbandwidth.

As illustrated in FIG. 3, the degree of acoustic pressure of theresonant frequency occurs as the fluid viscosity changes. By measuringthe variance the change status of the viscosity can be measured and thedesired fluid viscosity can be measured through compensation process.

Thus, fluid that serves as certain standards, for example water,measures the pressure sensed through the sensing part 180 according tothe increase of frequency of the actuating part 170, and the viscosityof the this water saves data after measuring the pressure followingfrequency by stage that increase 20%, 40%, 60%, 80%, 100%, asillustrated in FIG. 4.

Afterwards, the pressure data sensed from the sensing part 180 comparedto the frequency applied from the actuating part 170 on the fluid thatneeds measurement is obtained, and then the viscosity of the fluid thatneeds measurement is derived from the viscosity value that correspondsto the obtained data. The viscosity data that serves as a standard canbe obtained more precisely than the interval of 20% as in one of theembodiments.

Also, the frequency f_(L) and f_(H) of the pressure (0.707M) isobtained, which becomes 1/{square root over (2)} of the maximum pressure(M) when the frequency alters between before and after the viscositychange of the fluid as illustrated in FIG. 3, then it is substitutedinto Equation 4 below to derive the Q factor. The viscosity of the fluidcan be derived by using the Q factor, Equation 2 and Equation 3.

$\begin{matrix}{Q = \frac{f_{o}}{f_{H} - f_{L}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

In another aspect, the Helmholtz resonator is usually applied in acouple dozen to a couple hundred Hz where the character size of thesystem is greatly shorter than the frequency wavelength, also expressedka<<1. Here, the k is the wave number and a is a radius of the microchannel 140.

For this, one embodiment of the present invention uses MEMS process sothat it holds a very small and thin type compared to general viscometersand resonant frequency increases up to hundreds of thousands to tens ofmillions Hz of the system itself.

Therefore, this present device expands and interprets the frequencydomain so that is does not operate within the domain that does notsatisfy the frequency domain of the Helmholtz resonator, which is ka<<1.For this purpose, the Total Acoustic Impedance of this inventionexpresses Equation 5, and using the equation as shown in Equation 6where the reactance is 0 the resonant frequency can be derived.Z _(ac) Z _(mem1) +Z _(cal)+2Z _(end) +Z _(mc) +Z _(ca2) +Z_(mem2)  Equation 5

Each value for the impedance is shown below.

$Z_{{mem}\; 1} = \frac{K_{ac}^{{mem}\; 1}}{j\;\omega}$is the acoustic impedance of the first thin film 150,

$Z_{{mem}\; 2} = \frac{K_{ac}^{{mem}\; 2}}{j\;\omega}$is the acoustic impedance of the second thin film 160,

$Z_{{ca}\; 1} = {\frac{Z_{0}}{j\;\tan\;{kh}_{1}}\frac{1}{S_{1}}}$is the acoustic impedance of the first chamber 120,

$Z_{{ca}\; 2} = {\frac{Z_{0}}{j\;\tan\;{kh}_{2}}\frac{1}{S_{2}}}$is the acoustic impedance of the second chamber 120,

$Z_{mc} = {j\frac{Z_{0}\tan\;{kl}}{A}}$is the acoustic impedance of the micro channel 140,

$Z_{end} = {\frac{Z_{0}}{A}\left\{ {{R_{1}\left( {2\;{kr}_{c}} \right)} + {j\;{X_{t}\left( {2\;{kr}_{c}} \right)}}} \right\}}$is the acoustic impedance of the inlet 111 and outlet 112.

Furthermore, K_(ac) ^(mem1) and K_(ac) ^(mem2) are the AcousticStiffness of the first thin film 150 and second thin film 160respectively, h₁ and h₂ correspondingly represents the height of thefirst chamber 120 and second chamber 130, and

${{R_{1}\left( {2\;{kr}_{c}} \right)} = {1 - {\frac{2\;{J_{1}\left( {2\;{kr}_{c}} \right)}}{2\;{kr}_{c}}\mspace{14mu}\left( {J_{1}:{{Bessel}\mspace{14mu}{function}}} \right)}}},{{X_{1}\left( {2\;{kr}_{c}} \right)} = {\frac{2\;{H_{1}\left( {2\;{kr}_{c}} \right)}}{2\;{kr}_{c}}\mspace{14mu}\left( {H_{1}:{{first}\mspace{14mu}{order}\mspace{14mu}{struve}\mspace{14mu}{function}}} \right)}}$are each represented from Acoustic Impedance Z_(end).

If, the size and shape of the first chamber 120 and second chamber 130are the same, Z_(ac) can be more simply expressed, furthermore to findthe resonant frequency by taking the reactance of Z_(ac) can come upwith Equation 6 as shown below.

$\begin{matrix}{{{Im}\left( Z_{ac} \right)} = {{\frac{2\; Z_{0}}{A}\left\{ {{\frac{2}{2\;{kr}_{c}}\begin{bmatrix}{\frac{2}{\pi} - {J_{0}\left( {2\;{kr}_{c}} \right)} +} \\{{\left( {\frac{16}{\pi} - 5} \right)\frac{\sin\left( {2\;{kr}_{c}} \right)}{2\;{kr}_{c}}} +} \\{\left( {12 - \frac{36}{\pi}} \right)\frac{1 - {\cos\left( {2\;{kr}_{c}} \right)}}{\left( {2\;{kr}_{c}} \right)^{2}}}\end{bmatrix}} + \frac{\tan\;{kl}}{2}} \right\}} - \left\{ {{\frac{2\; Z_{0}}{\tan\;{kh}}\frac{1}{S}} + \frac{2\; K_{ac}^{mem}}{\omega}} \right\}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

Therefore, frequency of the k value that satisfies Im(Z_(AC))=0corresponds to the resonant frequency. By substituting a variable x forthese values, the follow Equation 7 can be derived.k _(n) =x _(x) (n:integer)  Equation 7

Resonant frequency can be derived by using Equation 8 below.

$\begin{matrix}{f_{1} = {\frac{k_{1}c_{o}}{2\;\pi} = \frac{x_{1}c_{o}}{2\;\pi}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

FIG. 5 is a graph comparing the difference of results between the casewhere ka<<1 for the Helmholtz resonator and the method that can beapplied to one embodiment of the present invention disregarding thevalue of ka.

When the calculation method of one embodiment of the present inventionholds a small radius (a) of the micro channel 140 so that the resonantfrequency (f) of the system is low, and satisfies the conditions ofka<<1, the Helmholtz resonator calculation method is approached, while,on the other hand, when the radius (a) of the micro channel 140 becomesgreater and the resonant frequency increases, and the assumption of theHelmholtz resonator calculation method, ka<<1, does not meet theconditions, the calculation method following the embodiment of thepresent invention should be applied.

FIG. 6 is a cross-sectional view of the second embodiment of the presentinvention illustrating a micro viscometer.

A micro viscometer 500 according to the second embodiment isstructurally similar to the first embodiment of a micro viscometer withseveral differences. Therefore, identical reference numerals are usedfor identical composition factors and explanations are not repeated.

Referring to FIG. 6, the second embodiment of a micro viscometer 500comprises multiple micro channels 140 on the body 110. Each microchannel 140 may have different lengths. Or, the lengths are identical sothat an acoustic pressure with the same phase angle and amplitudetransfers from each micro channel 140 and the sensing part 180 sensesthe acoustic pressure.

FIG. 7 is a graph of the absolute difference of acoustic pressureaccording to the number of micro channels when the viscosity of thefluid changes, based on the first embodiment and second embodiment ofthe present invention. FIG. 8 is a graph of the variation rate ofacoustic pressure according to the number of micro channels in identicalconditions with FIG. 7.

As it is shown from FIG. 7 and FIG. 8, when multiple micro channels areformed within the body of a micro viscometer, the variance of theacoustic pressure decreases compared to when a single micro channel isformed within the body interior, however, the acoustic pressureincreases.

For example, when the micro channel length is 3 mm in FIG. 7, and whenthe numbers of micro channels are 1 and 7 respectively, the acousticabsolute variance correspondingly turns out to be 0.05 Pa and 0.25 Pa.However, when checking the variance of acoustic pressure in FIG. 8 wherethe numbers of micro channels are 1 and 7 respectively, the acousticpressure shows similar values of 0.75 and 0.72 correspondingly.

Thus, measurements can be more greatly made for the signal of theacoustic pressure compared to the surrounding noise when measuring theacoustic pressure at the sensing part due to the effect that a greaterdegree of acoustic pressure is transferred as the number of microchannels increase.

Meanwhile, it is desirable for the first thin film and second thin filmto have identical resonant frequencies to increase the accuracy comparedto when measuring the viscosity of the fluid in an embodiment of thepresent invention that deal with a micro viscometer.

Furthermore, in order to accurately measure the viscosity of the fluideven more, the spatial structure of the chamber that forms the bodyinterior must be designed more acoustically. For this, FIG. 9 and FIG.10 are referenced to explain this matter.

FIG. 9 is a diagrammatic view of the chamber structure of a microviscometer according to one embodiment of the present invention andFIGS. 10 a-10 b are diagrammatic views of the first resonant frequencyand second resonant frequency that are transferred within the chamber ofa micro viscometer, respectively.

Referring to FIG. 9 and FIG. 10, the viscosity of the fluid within thebody can be accurately measured by the increase in the damping effect ofthe acoustic pressure, which is transferred through the first chamber120, within the micro channel 140 when the first resonant frequency thatoccurs from the thin film 150 transfers acoustic pressure to the firstchamber 120.

Namely, in order to transfer with the greatest degree of acousticpressure transferred to the first chamber 120 through the micro channel,the first resonance (a) must occur in the height direction of the firstchamber 120. Therefore, it is necessary for the height (H) of the firstchamber 120 to at least actually form a half wavelength that responds tothe first resonant frequency and the width of the first chamber 120should be shorter than the height of the first chamber 120 or the halfwavelength that corresponds to the first resonant frequency.

If the width of the first chamber 120 is longer than the height (H) ofthe chamber or the half wavelength corresponding to the first resonantfrequency, first resonance (a) occurs in the width direction of thefirst chamber 120 so that desirable acoustic pressure is not actuallytransferred through the micro channel 140. Like this, the height (H) andwidth (W) of the first chamber 120 depend on the first resonantfrequency of the thin film 150.

Furthermore, to make manufacturing process conditions simple in buildingone embodiment of the present invention according to a micro viscometer,the height (H) of the first chamber 120 should have an equal wavelengthcorresponding to the frequency in accordance with a second resonant (b)of the thin film 150.

The width (W) of the first chamber 120 should be at least smaller thanthe half wavelength of the second resonant frequency. This is becausewhen the second resonant frequency is larger than the length of the halfwavelength, the first resonant frequency of the thin film 150 with highdegree of the acoustic pressure in the width direction of the firstchamber 120 occurs which makes it actually hard for the acousticpressure transfer in the height direction of the first chamber that isthe wavelength direction of progress.

The structure of the chamber as above is not shown. However, it canidentically used not only for the first chamber 120 of the actuatingpart but also the second chamber 130 of the sensing part.

Meanwhile, to measure the viscosity of the fluid more accurately it isnecessary to cancel the noise occurring due to the electric effectbetween the actuating part 170 and the sensing part 180 when a microviscometer operates.

FIG. 11 is the electric circuit of a micro viscometer according to oneembodiment of the present invention.

As illustrated, a micro viscometer constructs the electric circuit bydividing into the actuating part and sensing part. When applying voltagein the actuating part at this moment the current following the voltageactually should not flow into sensing part so that the viscosity of thefluid can be derived from the genuine acoustic pressure.

Due to the characteristics of the substrate 113, when the voltageapplied to the actuating part is a direct current signal the electricimpedance becomes infinite so that the current following the appliedvoltage of the actuating part does not flow into the sensing part,however, when the voltage applied on the actuating part is a alternatingcurrent the impedance becomes lower which brings the resistance of thesubstrate to decrease.

The current following the voltage, which is applied on the actuatingpart, flows into the sensing part which causes inaccurate measurementsof viscosity of fluids due to an electrical noise included in theacoustic pressure measurement of the sensing part.

Therefore, as shown in FIG. 12, in a micro viscometer according to oneembodiment of the present invention, electrical separation of theactuating part 170 from the sensing part 180 is necessary.

Physically, a thin film 150 has a trench S1 formed between the firstchamber 120 and second chamber 130 so that the actuating part 170 andsensing part 180 actually has electrical separation, and the main trench(S1) extends to a portion of the substrate 113 positioned on the thinfilm bottom. The number of main trench (S1) can be at least one.

Preferably, the main trench (S1) is formed on the substrate 113 and cutsthrough the thin film 150 and has a depth of more than ½ of thethickness of the substrate 113.

When applying voltage on the actuating part 170 or sensing part 180,noise can be measured with the measurement of the viscosity of fluidfrom acoustic pressure from the effect of the applied current in betweenthe first electrode 175 and second electrode 173 of the actuating part170 or in between the third electrode 185 and fourth electrode 183 ofthe sensing part 180.

To prevent this, the thin film should provide electrical separationbetween the first electrode 175 and second electrode 173 or between thethird electrode 185 and fourth electrode 183. In one embodiment, asupporting (or auxiliary) trench (S2) can be constructed for electricalseparation between the first electrode 175 and second electrode 173 orbetween the third electrode 185 and fourth electrode 183 of the thinfilm 150.

Like this, a micro viscometer according to one embodiment of the presentinvention, enables the measurement of viscosity not only in liquid butalso gas, and since the size of this viscometer holds its merits bybeing itself the smallest model, not only does it become used as anindependent equipment exclusively for viscosity but also allows accurateviscosity measurement of the fluid when included as a component ofanother equipment.

Furthermore, as the interest on the bio technology has risen, theapplication has become various, in measurements for such as viscosityfor various fluids within the living body, including the viscositymeasurement on blood and viscosity and variance measurement of amplifiedDNA due to Micro PCR, etc.

In addition, this present invention, regarding a micro viscometer, canmeasure the viscosity and variance with only a minimal amount of fluidby utilizing MEMS (Micro-Electro Mechanical Systems) structure so thatmeasuring hardly obtainable or high cost reagents or gas is possible.Also, due to the fact that gravity does not affect the device theviscometer can disregard the location or direction of placement.Furthermore, the viscometer quickly and efficiently measures theviscosity with a character of small size that promotes the use as anindependent device and also does not take much space as a component ofanother device.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described examples are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the meets and bounds of theclaims, or equivalences of such meets and bounds are therefore intendedto be embraced by the appended claims.

What is claimed is:
 1. A micro viscometer, comprising: a body including;a first chamber, an inlet for introducing a fluid into the firstchamber, a second chamber, an outlet for discharging a fluid from thesecond chamber, a cover, and a substrate secured to the cover and havinga plurality of micro channels for fluid communication between the firstchamber and the second chamber; a first thin film disposed on one sideof the first chamber and adapted to vibrate with the fluid within thefirst chamber; a second thin film disposed on one side of the secondchamber and adapted to vibrate with the fluid within the second chamber;an actuating part for applying vibration onto the fluid in the firstchamber by conducting vibration through the first thin film; and asensing part for sensing at least one of vibration or pressure of thefluid in the second chamber, wherein each of the first thin film and thesecond thin film includes a silicon wafer and an insulator attached to atop side and bottom side of the silicon wafer.
 2. The micro viscometerof claim 1, wherein a resonant frequency of the first thin film issubstantially identical to a resonant frequency of the second thin film.3. The micro viscometer of claim 1, wherein at least one side within theinlet, the outlet, the first chamber, the second chamber and theplurality of micro channels is coated with a hydrophilic layer.
 4. Themicro viscometer of claim 1, wherein the plurality of micro channelshave substantially a same length.
 5. The micro viscometer of claim 1,wherein the actuating part includes a first piezoelectric layer andfirst electrodes disposed on two sides of the first piezoelectric layer.6. The micro viscometer of claim 1, wherein the sensing part includes asecond piezoelectric layer and second electrodes disposed on two sidesof the second piezoelectric layer.
 7. The micro viscometer of claim 1,wherein the substrate includes a silicon layer and the cover is formedof a transparent material.